Stereoscopic 3D images are visible in such a manner that images prepared for the left eye and the right eye are viewed separately by the left and right eyes of an individual, so that the images are recognized as a three-dimensional image. Various 3D display technologies have been proposed, and they largely fall into two types: those that require special glasses, and those that are visible with the naked eye. A classical type of special glasses uses color filters, while special glasses currently proposed use wavelength selection filters or polarizing filters. The method using a polarizing filter includes, for example, an active system and a passive system. The active system is also called a time-division method, in which images for the left and right eyes are sequentially displayed in a time-division manner, and a viewer views the images through special glasses with polarizing filters that are opened and closed in synchronization with the switching of the images, so that the images are recognized as a three-dimensional image. On the other hand, the passive system is a way to show images for the left and right eyes by two orthogonal polarized light beams or circularly-polarized light beams with different directions of polarization on the left and right sides, and filter the images through special glasses with polarizing filters having orthogonal polarization axes on the left and right sides or with circular polarizations having different directions of polarization, so that the images are recognized as a stereoscopic image. Such 3D images can be provided not only in movies, but also in various displays, such as liquid crystal display devices (NPL 1).
In contrast, liquid crystal display (LCD) devices display images in such a manner that a liquid crystal cell, which is controlled to be on or off by a change in voltage, controls light passing through two polarizers. A liquid crystal display device comprises, as main components, a backlight light source, two polarizers, and a liquid crystal cell disposed between the two polarizers, and optionally comprises various optical functional films, such as a lens sheet and diffusion sheet.
A polarizer, which is a constituent member of an LCD, has a characteristic of selectively allowing only polarized light amplified in a specific direction to pass through. Accordingly, the light emitted from the LCD is polarized. A polarizer generally comprises a polarizing film made of stretched polyvinyl alcohol (PVA) and a dichromatic dye, such as iodine, and protective films that protect both sides of the polarizing film. In terms of optical characteristics, triacetyl cellulose films (TAC films) that are not affected by polarization and do not have birefringence have been mainly used as the protective films. Along with the recent trend toward thinner LCDs, there is a demand for reducing the thickness of the polarizers. However, when the thickness of a TAC film is reduced, problems such as insufficient mechanical strength and deteriorated moisture permeability occur. Moreover, since TAC films are very expensive, inexpensive alternative materials are strongly desired.
Accordingly, in order to reduce the thickness of the polarizers, there is a proposal to use oriented films made of a polyester resin or a polycarbonate resin as protective films in place of TAC films, so that high durability can be maintained even though the thickness of the films is low (PTL 1 to PTL 3). These oriented films have excellent mechanical strength and durability, but have birefringence, unlike TAC films. When polarized light passes through a film having birefringence, optical deformation occurs, and consequently brightness is likely to be reduced. For this reason, when an oriented film and a polarizing film were laminated to form a polarizer, it was necessary to laminate the oriented film and the polarizing film so that the orientation axis of the oriented film was parallel to the polarization axis of the polarizing film, in terms of preventing a decrease in brightness or reducing variations in the polarization state due to birefringence (PTL 3).